The present invention is directed to bicycles and, more particularly, to a torque sensor for a bicycle bottom bracket assembly.
In power-assisted bikes, which are bicycles in which an electric motor is used as auxiliary motive power, the auxiliary motive power is delivered in accordance with drive torque. Consequently, such power-assisted bikes are provided with torque sensors for sensing the drive torque. These sensors are installed, for example, in the bottom bracket axle assembly (which supports the pedals and crank arms) as shown in Japanese Unexamined Patent Applications (Kokai) 8-297059 and 8-313375. Such torque sensors are used not only for controlling the motor output of power-assisted bikes but also for controlling the shift timing of automatic shifting devices, for example.
The torque sensor disclosed in the first document comprises a drive shell fixedly fitted over the bottom bracket axle and provided with a chainwheel at one end, a magnetic material applied to the drive shell, and a coil unit mounted around the outside of the magnetic material of the bottom bracket. In such a torque sensor, the magnetic material develops a strain proportional to the torque when torsional force is generated by the rotation of the cranks. When strain is created in the magnetic material, the magnetic permeability of this material varies in accordance with the strain, thus changing the voltage of the coil unit. The torque is sensed based on the changes in this voltage.
Since this torque sensor senses a torque that varies with the strain of the magnetic material, it requires complex electrical circuitry for sensing very small strains. Additionally, the accuracy with which the magnetic material or the coil unit is mounted must be kept at a high level in order to measure such small strains. The sensor is therefore difficult to mount. Furthermore, the need to mount a coil unit in the bottom bracket makes it impossible to mount a bottom bracket axle assembly having a torque sensor in the bottom bracket of a standardized bicycle and fails to provide interchangeability with commercially available bottom bracket axle assemblies.
The torque sensor disclosed in the second document comprises a follower disk that rotates integrally with the chainwheel and that is rotatably mounted on the bottom bracket axle, a drive disk that rotates together with the bottom bracket axle, a spring plate for connecting the two disks, and a proximity switch facing the two disks and designed to sense the phase difference between the two disks. With such a torque sensor, the rotation of the cranks is transmitted to the chainwheel via the bottom bracket axle, drive disk, spring plate, and follower disk.
Unfortunately, this torque sensor requires that two disks be provided around the bottom bracket axle and that a proximity switch be installed facing these disks, thus complicating the structure of the bottom bracket axle assembly and increasing its radial dimensions. This, in turn, requires a larger bottom bracket on the bicycle. Thus, a bottom bracket axle assembly having this torque sensor cannot be mounted on the bottom bracket of a standardized bicycle, and it is impossible to provide interchangeability with commercially available bottom bracket axle assemblies.
The present invention is directed to a torque sensor for a bicycle bottom bracket assembly that has a compact structure, is easy to install, and which may be used with existing and commercially available bottom brackets. In one embodiment of the present invention, a torque sensor for a bicycle bottom bracket assembly having a bottom bracket axle includes an axle supporting member for supporting the axle for rotation around a support axis. The axle supporting member has a first sensor mounting location, and a first pressure sensor is provided for placement at the first sensor mounting location. In a more specific embodiment, the axle supporting member includes a second sensor mounting location and a second pressure sensor is provided for placement at the second sensor mounting location. The second sensor mounting location may be spaced apart from the first sensor mounting location in the direction of the support axis. In this case the second sensor mounting location may face the first sensor mounting location in the direction of the support axis or may be disposed diagonally across from the first sensor mounting location in the direction of the support axis. Alternatively, the second sensor mounting location may face the first sensor mounting location in the radial direction of the axle supporting member.
In an even more specific embodiment, the axle supporting member may include a second sensor mounting location spaced apart from the first sensor mounting location in the direction of the support axis, a third sensor mounting location spaced apart from the first sensor mounting location in a radial direction of the axle supporting member, and a fourth sensor mounting location spaced apart from the third sensor mounting location in the direction of the support axis. A second pressure sensor may be provided for placement at the second sensor mounting location, a third pressure sensor may be provided for placement at the third sensor mounting location, and a fourth pressure sensor may be provided for placement at the fourth sensor mounting location. If desired, the second sensor mounting location may face the first sensor mounting location in the direction of the support axis, the fourth sensor mounting location may face the third sensor mounting location in the direction of the support axis, the third sensor mounting location may face the first sensor mounting location in the radial direction of the axle supporting member, and the fourth sensor mounting location may face the second sensor mounting location in the radial direction of the axle supporting member.
In a more specific embodiment of the invention directed to a more complete portion of the bottom bracket assembly, a torque sensor for the bicycle bottom bracket assembly includes an axle having an axle axis, a first bearing including a plurality of first rollers disposed on the axle, and a second bearing including a plurality of second rollers disposed on the axle. The first bearing is spaced apart from the second bearing in the direction of the axle axis. A tubular bearing housing surrounds the axle so that the first bearing and the second bearing are disposed between the axle and the bearing housing and so that the axle is rotatably supported in the bearing housing. A first tubular member is disposed at a first end of the bearing housing, and a second tubular member is disposed at a second end of the bearing housing. A first pressure sensor is disposed between the first tubular member and the bearing housing.
If desired, a second pressure sensor may be disposed between the second tubular member and the bearing housing. More specifically, the first tubular member may be disposed about an outer peripheral surface of the bearing housing, and the second tubular member may be disposed about the outer peripheral surface of the bearing housing. In such a case the first pressure sensor may be disposed between an inner peripheral surface of the first tubular member and the outer peripheral surface of the bearing housing, and the second pressure sensor may be disposed between an inner peripheral surface of the second tubular member and the outer peripheral surface of the bearing housing. The second pressure sensor may be located diagonally across from the first pressure sensor in the direction of the axle axis, or else the second pressure sensor can face the first pressure sensor in the direction of the axle axis.
In a further embodiment of this type, a third pressure sensor may be disposed between the inner peripheral surface of the first tubular member and the outer peripheral surface of the bearing housing, and a fourth pressure sensor may be disposed between the inner peripheral surface of the second tubular member and the outer peripheral surface of the bearing housing. The third pressure sensor may face the first pressure sensor in a radial direction of the bearing housing, and the fourth pressure sensor may face the second pressure sensor in the radial direction of the bearing housing.
In an even further embodiment of the present invention, a first sensor mounting member having a first sensor mounting location may be provided, wherein the first sensor mounting member is disposed between the bearing housing and the first tubular member. In this case the first pressure sensor is disposed at the first sensor mounting location. If the first pressure sensor is disposed radially outwardly of the first sensor mounting member, then a first sensor pressing member may be disposed between the first pressure sensor and the first tubular member. As with the above embodiments, a second sensor mounting member having a second sensor mounting location may be provided, wherein the second sensor mounting member is disposed between the bearing housing and the second tubular member. In this case the first pressure sensor may be located diagonally across from the second pressure sensor in the direction of the axle axis. If the first pressure sensor is disposed radially outwardly of the first sensor mounting member and the second pressure sensor is disposed radially outwardly of the second sensor mounting member, then a first sensor pressing member may be disposed between the first pressure sensor and the first tubular member, and a second sensor pressing member may be disposed between the second pressure sensor and the second tubular member.
If desired, the first sensor mounting member and the second sensor mounting member each may have an outer peripheral surface in a shape of an octagon, and the first sensor pressing member and the second sensor pressing member each may have an inner peripheral surface in a shape of an octagon. A first flat side of the first sensor mounting member faces the first pressure sensor, and a second flat side of the second sensor mounting member faces the second pressure sensor. Two flanking sides of the outer peripheral surface of the first sensor mounting member adjacent to and flanking the first flat side may be spaced apart from the inner peripheral surface of the first sensor pressing member, and two diametrically opposite spaced sides of the outer peripheral surface of the first sensor mounting member diametrically opposite the two flanking sides of the first sensor mounting member may be spaced apart from the inner peripheral surface of the first sensor pressing member. Similarly, two flanking sides of the outer peripheral surface of the second sensor mounting member adjacent to and flanking the second flat side may be spaced apart from the inner peripheral surface of the second sensor pressing member, and two diametrically opposite spaced sides of the outer peripheral surface of the second sensor mounting member diametrically opposite the two flanking sides of the second mounting member may be spaced apart from the inner peripheral surface of the second sensor pressing member. Additionally, two diametrically opposite sides of the outer peripheral surface of the first sensor mounting member between the two flanking sides of the first sensor mounting member and the two diametrically opposite spaced sides of the first sensor mounting member may contact the inner peripheral surface of the first sensor pressing member, and two diametrically opposite sides of the outer peripheral surface of the second sensor mounting member between the two flanking sides of the second sensor mounting member and the two diametrically opposite spaced sides of the second sensor mounting member may contact the inner peripheral surface of the second sensor pressing member.
In yet another embodiment, the first sensor pressing member may have a curved outer peripheral surface facing an inner peripheral surface of the first tubular member. Such a curved surface helps to distribute the pressure exerted between the first tubular member and the sensor pressing member evenly to the pressure sensor.